1. Field of the Invention
This invention relates to a developing device using one-component magnetic toner as developer.
2. Description of the Prior Art
As a developing method using one-component magnetic toner, the developing method using electrically conductive magnetic toner disclosed in U.S. Pat. No. 3,909,258 is known and has been widely used. However, in such developing method, the toner must essentially be electrically conductive and with the electrically conductive toner, it has been difficult to have a toner image on a latent image bearing member transferred to a final image supporting member (for example, plain paper or the like) by the utilization of an electric field (although the reason therefor has not yet been clarified sufficiently).
The assignee of the present invention has previously proposed novel developing methods which eliminate such disadvantage peculiar to the conventional developing method using one-component magnetic toner. They are disclosed, for example, in U.S. application Ser. Nos. 58,434 abandoned in favor of Continuation U.S. application Ser. No. 264,516 filed May 18, 1982 and U.S. Pat. No. 4,292,387. These methods comprise uniformly applying insulative magnetic toner onto a cylindrical developer supporting member having a magnet therewithin, causing the same to be opposed to a latent image bearing member without bringing it into contact with the latter, thereby effecting development. At this time, a low-frequency alternating voltage is applied between the developer supporting member and the substrate conductor of the latent image bearing member to cause reciprocal movement of the toner between the developer supporting member and the latent image bearing member, whereby it is possible to accomplish good development which is fogless and excellent in reproduction of tone gradation and free of thinning at the ends of the image. In these developing methods, the toner is an insulator and this facilitates the image transfer.
In such developing methods, it is very important to uniformly apply the toner onto the developer supporting member. That is, if the toner layer on the developer supporting member becomes excessively thick, not only the toner is rubbed against the latent image bearing member but also the frictional charging of the toner due to the friction between the toner and the developer supporting member tends to become insufficient. On the other hand, if the toner layer becomes thin, the amount of toner used for the development becomes deficient and thus, the density of the developed image becomes unsatisfactory.